Basic Testing Procedures

[Sintra]

so Ze is at the main incomer and Zs can be measured at every other fitting,and what does this tell you,the Zs that is?

The Zs figure obtained will let you know whether a protective device will operate in the required time under fault conditions.

 

[vbyrne]

Ze is the test done at the main incomer, with the main earth dis-connected from MAIN EARTH TERMINAL with the mains still on is that right.My other question is , is it right saying that I can measure Zs at every fitting

 

[vbyrne]

The Zs figure obtained will let you know whether a protective device will operate in the required time under fault conditions.

so there must be a table of numbers that the result must be under to be ok

 

[Sintra]

Ze is the test done at the main incomer, with the main earth dis-connected from MAIN EARTH TERMINAL with the mains still on is that right.My other question is , is it right saying that I can measure Zs at every fitting

Zs only needs to be tested at the last point on every circuit as you will have previously tested R1+R2 at every accessory prior to energising.

 

[vbyrne]

Zs only needs to be tested at the last point on every circuit as you will have previously tested R1+R2 at every accessory prior to energising.

Thanks ,so the test is for the circuit and not for every fitting

 

[vbyrne]

Yes at this stage the main earthing conductor will have been reconnected back into the MET the main switch will be in the open (off) position. Test carried out at incoming side of main switch.

what do I do if I can not turn off the power to carry out this test and what happens if I do the test with the power on in the building.

 

[Sintra]

so there must be a table of numbers that the result must be under to be ok

Yes there is a table in bs7671

Thanks ,so the test is for the circuit and not for every fitting

Correct

what do I do if I can not turn off the power to carry out this test and what happens if I do the test with the power on in the building.

The installation NEEDS to be isolated for Ze as main earthing conductor is disconnected. If you can not isolate then this needs to be noted as a limitation but only on a PIR.

As for PFC this could be done with the installation live as all earthing and bonding will be in place.

 

[Guest123]

Get yourself a copy of Guidance Note 3, and have a good read.

 

[vbyrne]

Get yourself a copy of Guidance Note 3, and have a good read.

I like talking to you guys about these things ,its much more fun than reading a book but I will have to get myself guidance note 3 as the one I have is out of date I think, it is yellow in colour .Do you know any where I can get GN3 and BS7671 a bit cheaper

 

[vbyrne]

Yes there is a table in bs7671



Correct




The installation NEEDS to be isolated for Ze as main earthing conductor is disconnected. If you can not isolate then this needs to be noted as a limitation but only on a PIR.

As for PFC this could be done with the installation live as all earthing and bonding will be in place.

I ll tell you what I'm doing, I am installing new circuits and breaking into exsisting rings ,when I install a new circuit I issue a New installation cert and when I tamper with a ring I issue a Minor works cert,but the thing is I am doing this in a very large store and the power can not be turned off so I can not do my Ze so I think I put this down as a limatation and just do PFC or if I can get my hands on previous test sheets issued can I use them?

 

[macrylinda1]

Beg to differ here IMO the safe isolation must be done prior to the Ze test as you are removing the main earthing conductor to the installation. I stated that the Ze test had to be done with the supply switched off not that it was a dead test

The actual supply is not switched off, the installation past the main breaker is switched off granted but not the supply. Anyone just about to take the 2391 practical may be confused as books including GN3 and OSG use the CRIPLER method and this is the way i've been taught to test within my 2391 course;

Dead tests:

Continuity of circuit protective conductors
Ring final circuit conductor continuity
Insulation resistance testing
Polarity

 

[WayneL]

The actual supply is not switched off, the installation past the main breaker is switched off granted but not the supply. Anyone just about to take the 2391 practical may be confused as books including GN3 and OSG use the CRIPLER method and this is the way i've been taught to test within my 2391 course;

Dead tests:

Continuity of circuit protective conductors
Ring final circuit conductor continuity
Insulation resistance testing
Polarity

Except that you don't have to follow any particular order in the 2391, as it's a PIR that you are completing, not an Initial Verification.

You can basically test in the order that suits you best.

 

[RexT]

Hi Sintra,

Just want to say thanks for the useful post, I couldnt get to the thanks button.

Best wishes

Rex

 

[Stradders]

Reading that makes me want it even more!

Sad i know

 

[BillyBoBob]

Dead tests:

Continuity of circuit protective conductors
Ring final circuit conductor continuity
Insulation resistance testing
Polarity

Live Tests:

Loop impedance test external (Ze)
Earth fault loop impedances (Zs)
RCD testing

Just a note I was shown this and it really helped. It's vey similar.

C.R.I.P.P.E.L.D (main point to notice E & L are the wrong way round)

Continuity of C.P.C's inc main and supplementary bonding conductors

Ring final continuity

Insulation resistance

Polarity (dead)
>Earth electrode test if a TT system
Polarity (Live) inc phase rotation at origin of the installation

Externals Ze inc PFC at origin

Loop impedance Zs inc phase rotation and PFC both taken at the load

Devices inc RCD/RCBO and fuctional testing of both On-load and Off-load switching devices